Applicant claims the priority of Japanese patent application, Ser. No. 11-105657, filed Apr. 13, 1999.
The present invention relates to a fuel supplying structure of a carburetor for an internal combustion engine which is loaded on a portable working machine such as a reaping machine or a ventilator, particularly a carburetor which can effectively discharge fuel vapor or air within a constant pressure fuel chamber out from the carburetor and back to a fuel tank to assure a an continuous reliable amount of fuel to the engine.
The engine loaded in a portable working machine generates great vibration due to its downsizing and high speed revolution. Therefore, because of the heat or vibration generated during engine running, fuel vapor is generated in not only a carburetor but also in a fuel passage from a fuel tank to the carburetor. This may lead to lean-burn continuous abnormal combustion, thus leading to a possible slump of a rotary speed of the engine and possible stoppage of the engine.
In order that the carburetor can continue running irrespective of a status or position change of the engine in any direction, a fuel supplying mechanism of the carburetor includes a constant-pressure fuel chamber partitioned by a diaphragm, for example, rubber or other elastic material. The fuel path or fuel system from the fuel tank to an intake passage via a diaphragm fuel pump, constant-pressure fuel chamber and a fuel nozzle is hermetically sealed with no air vent to the ambient atmosphere. Gasoline serving as the fuel that is vaporized due to heat or vibration of the engine while it flows from the fuel tank to the intake path via the diaphragm fuel pump, constant-pressure fuel chamber, fuel path and fuel nozzle, is stored as fuel vapor in the constant-pressure fuel chamber or fuel path.
The fuel vapor generated in the fuel system, which is formed in a hermetically sealed structure, may be finally supplied to the intake path through the fuel nozzle. The vapor may accompany the liquid fuel and the engine may still run properly. However, if excessive amounts of the fuel vapor are generated, only the fuel vapor maybe supplied to the fuel nozzle. Thus, the engine is subject to acceleration-running or sloping-running status. The supply of fuel to the engine is temporarily stopped so that the speed of the engine may abruptly lower and the engine may be stopped. Once the engine is stopped and when the engine is restarted again, the state where only the fuel vapor is supplied to the intake path continues, thus greatly impairing the performance of the engine. The malfunction of the engine described above is apt to occur during high-loaded running, particularly under a heated condition such as under a burning sun in summer.
In view of the above problem, what is needed is a fuel vapor discharging structure for a carburetor which can always, during engine running, discharge the fuel vapor that builds up in a constant-pressure fuel chamber in a carburetor.
In accordance with the present invention, there is provided a fuel supplying mechanism for a carburetor in which fuel in a fuel tank is supplied to a constant-pressure fuel chamber through a flow-in valve by a fuel pump which is preferably driven by the pulsating pressure of the intake air in an engine, and further supplied from the constant-pressure fuel chamber to a fuel nozzle projecting into an air intake passage. The fuel supplying mechanism has a purge pump preferably driven by the pulsating pressure of the intake air in the engine. A plurality of vapor reservoir chambers are provided at a higher position at the ceiling wall of the constant-pressure fuel chamber than the inlet of the fuel nozzle. The fuel vapor in the plurality of vapor reservoirs is sucked by the purge pump and discharged out of the fuel chamber. Preferably, the vapor is returned to the fuel tank.
It is also desirable that both the fuel pump and the purge pump are operated by a respective diaphragm. The respective diaphragms are formed from different sections of a single membrane mounted in the carburetor.
A throttle is provided at an outlet path of the purge pump to suppress the flow-out of the fuel as well as the fuel vapor from the constant-pressure fuel chamber into the fuel tank through the purge pump and assure the fuel flowing from the constant-pressure fuel chamber to the fuel nozzle. A check valve is provided in an outlet passage of the purge pump so that the fuel vapor or fuel which is purged from the constant-pressure fuel chamber to the fuel tank is prevented from returning to the constant-pressure fuel chamber via the purge pump.